As is known to all, LED illumination has irreplaceable advantages. It is energy saving, has very low power consumption, has a nearly 100% electro-optical power conversion, can save more than 80% of energy with the same illumination efficiency compared with the traditional light source, and has a long lifespan. In view of the above advantages, people more and more frequently use LEDs as light sources, for example, numerous LED retrofit lamps in the market. Such LED retrofit lamps have a profile of a traditional light source such as an incandescent lamp or lamp tube, such that they, as light sources, can be adapted to the existing illumination systems. In the current illumination devices, the LED light sources are widely used.
However, due to the particular configuration of the LED light sources, a single LED light source cannot achieve 360° omnidirectional illumination. In order to achieve omnidirectional illumination, multiple solutions are used in the prior art, for example, with a quite complicated heat sink structures with many LED light sources placed all around the heat sink structures, with phosphor light bulbs, with light guide structures, with reflecting structures inside the bulb. However, various defects exist in the above solutions, for example, having complicated structure, being difficult to assemble, having high cost, or having very low efficiency. In addition, the LED retrofit lamps further need to provide uniform light distribution over a very large area. Especially in the US market, the strict Energy Star criteria have to be met for the luminance intensity distribution.